A rolling material may not be processed accurately by means of a roller dice device, in a case where circumferential rolling grooves of a pair of rolling rollers are displaced relative to each other in a width direction of the grooves. A roller dice device is disclosed in JP10-225713A, in which positions of roller axes of rolling rollers are fixed in an axial direction thereof so as not to allow displacement of circumferential rolling grooves relative to each other in a width direction of the grooves. Further, according to JP2007-220490, in order to form a wire, having a substantially circular-shaped cross-section, into a rectangular wire, having a substantially rectangular-shaped cross-section, a first pair of rollers forms two sides, facing each other in a radial direction of the wire, and a second pair of rollers forms the other two sides, facing each other in a radial direction of the wire.
According to JP10-225713A, when a rolling material moves through a rolling portion, the rolling material contacts the circumferential rolling grooves. At that time, a reaction force, which includes a component force in the axial direction of the rolling rollers, may be applied to each of the circumferential rolling grooves of the pair of rolling rollers. Consequently, moment is generated, which causes displacement of outer circumferential surfaces of the rolling rollers relative to each other in the axial direction of the roller. Accordingly, the circumferential rolling grooves may easily be displaced relative to each other in the width direction of the grooves. Further, according to JP2007-220490, in order to form the rectangular wire, having the rectangular-shaped cross-section, the first pair of rollers for rolling longer sides may include greater thickness and greater rigidity than the second pair of rollers for rolling shorter sides. However, in order to form a rectangular wire, whose shorter sides are narrow in width (for example, a rectangular wire whose shorter sides are 1 mm or less in width), a width of a pair of rollers for rolling the shorter sides is required to be narrow so as to correspond to the width of the shorter sides. Consequently, a rigidity of the pair of rollers for rolling the shorter sides may be reduced, and as a result, accuracy in forming the rectangular wire may be reduced.
A need thus exists for a synchronous motor control device that is not susceptible to the drawback mentioned above.